Another plume was also found on Europa, one of Jupiter's moons that's covered in ice and has twice as much ocean as Earth underneath that surface.
"With this research we are making a big step forward to answering the question is there life out there", Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate at Headquarters in Washington, said during the press conference.
Soon after the Cassini orbiter began circling Saturn in 2005 it discovered water plumes venting into space from cracks at the moon's south pole.
Enceladus, which is 502 kilometres (312 miles) across, is one of numerous moons orbiting Saturn, the largest of which, Titan, is bigger than the planet Mercury.
Could there be life under the icy surface of Saturn's moon Enceladus?
Scientists suspect that this is what's happening on Enceladus, hence the presence of molecular hydrogen in the plumes.
"We now know that Enceladus has nearly all of the ingredients you would need to support life as we know it on Earth", she continued.
NASA may have found the ingredients for sustainable life on Saturn's moon, Enceladus. As we still haven't ever found life anywhere but on Earth, though, finding anything living at all in another location, even if it's not full-blown space whales, would be a huge discovery.
The Cassini spacecraft detected the hydrogen in the plume of gas and icy material spraying from Enceladus during its last, and deepest, dive through the plume. This plume is correlated with a thermal spot of interest, and if the two are connected, says NASA, it could help shed light on the nature of the moon's activities.
The announcement will coincide with results from the Hubble Space Telescope, which has been looking for water on planets outside the solar system, and in particular for evidence that they contain primitive life, such as the unexpected creation of methane.
The discovery of this chemical energy source means Enceladus is now the very best place to look for life outside of Earth, with conditions that could be just right for alien microbes to survive.
"Enceladus is high on the list in the solar system for showing habitable conditions", said lead author Hunter Waite.
We've got the Cassini spacecraft to thank for the new findings, as the probe has been busy taking measurements around Saturn and Enceladus since 2004. New observations from NASA's Galileo spacecraft suggests Europa's plume, like the plumes on Enceladus, is associated with warmer temperature readings.
The Europa Clipper is set to launch in the 2020s and will make close flybys to Europa to study the oceans there to determine whether or not the same thing is happening there as on Enceladus, and importantly whether or not the moon could possibly support life.